The present invention relates to the selective removal of substances from liquid solutions and/or suspensions and, more particularly, to the chillproofing of beverages such as beer.
For many years it has been known that, unless specially treated, stored beers will undergo reactions which result in the production of insoluble compounds and complexes which impart a distinct haze or turbidity to the beer, most noticeable at low temperatures (e.g., below about 20.degree. C.), which is perceived by the consumer as undesirable. That portion of the haze which is exhibited at low temperatures but which disappears at temperatures at or above 20.degree. C. is referred to in the art as "chill haze", while any remaining haze at these temperatures is referred to as "permanent haze". As the storage time in kegs, cans or bottles increases, the amount of chill haze exhibited also increases and can also lead to an increase in the amount of permanent haze (i.e., a greater amount of the haze exhibited at low temperatures does not disappear at temperatures at or above 20.degree. C.).
The preference of beer consumers, particularly in the United States, for drinking beer at very cold temperatures makes the problem of dealing with chill haze extremely important. This is further attenuated by the fact that present day mass manufacturing and marketing conditions can result in long periods of time (often as long as six months to a year) between the manufacture of beer and its ultimate consumption. As a consequence, it is well known in the art to seek to "chillproof" beer, i.e., to take steps which lead to elimination or substantial reduction of chill haze.
Chill haze in beer is generally understood to comprise reaction products of materials such as proteins, polyphenols and carbohydrates, which materials are introduced into the beer via the raw ingredients used in beer making and/or result from the fermentation process. The interaction of proteins and polyphenols in beer plays the major role in chill haze formation and, as a consequence, most prior art attempts to eliminate or reduce chill haze focus upon either protein or polyphenol components.
Proposals for the chillproofing of beer have been many. One potential solution is to hold beer for an extended period of time at conditions which promote haze formation, making it possible to then physically remove the formed compounds prior to bottling, canning or other like packaging. This is hardly a practical solution, however, since it greatly increases the time and cost involved in beer making per se. Another similar approach to chillproofing is to accelerate formation of haze by overtly adding polyphenols such as tannins, anthocyanogens or gelatin-rutin complexes to the beer and then filtering the beer to remove the formed compounds prior to bottling, etc. A still further approach which has been suggested is to choose and/or pre-treat the raw materials used in beer making in an attempt to limit the concentration of, e.g., polyphenols introduced into the beer during the beer-making process.
By far the most prevalent approach to the problem of chill haze, however, is the treatment of beer with agents to partially remove or otherwise eliminate either proteins or polyphenols from the beer prior to bottling, canning or other like packaging operation, and thereby eliminate one of the reactants involved in haze formation. One of the earliest known methods for chillproofing beer in this manner involved contact of the beer with proteolytic enzymes to hydrolyze proteins (U.S. Pat. No. 995,820 to Leo Wallerstein). However, as a result of consumer concerns regarding additives in general and stricter labelling laws requiring listing of additive materials such as proteolytic enzymes which remain in the final product, the art moved in the direction of utilizing solid absorbent materials to remove either proteins or polyphenols from beer, in which the absorbent (and bound protein or polyphenol) is removed from the beer by filtering prior to bottling or canning. For example, U.S. Pat. No. 2,416,007 discloses the use of a magnesium silicate clay as an absorbent for proteins in beer, while U.S. Pat. No. 3,251,693 describes the use of synthetic calcium, magnesium and zinc silicates for chillproofing beer. Materials such as Nylon-66, polyvinyl polypyrrolidone and other polyamides are known for use in chillproofing of beer for their ability to sorb polyphenols (particularly anthocyanogens). See, e.g., U.S. Pat. No. 2,688,550. In addition, various polymeric derivates of silicic acid are known for use in sorbing proteins in chillproofing processes.
A major consideration in this approach to chillproofing, however, is that materials within the class of proteins and polyphenols are important contributors to the desirable foaming and taste characteristics of beer. Hence, absorbent materials used as chillproofing agents must exhibit a degree of selectivity in removing protein or polyphenolic haze precursors. In addition, chillproofing agents must be inexpensive relative to the overall cost of making beer, and must effect the requisite degree of absorption within a reasonably short residence time with the beer.
Accordingly, despite the variety of chillproofing agents known in the art, research and development continues in search of agents useful for such purposes which offer advantages in terms of expense and/or selectivity over known materials.